Nutritive value of maralfalfa grass (Pennisetum purpureum x Pennisetum glaucum) under defoliation conditions

Maralfalfa grass (Pennisetum purpureum x Pennisetum glaucum) is a high quality tropical grass which has potential as forage for ruminants but questions remain about quality response to defoliation management. A plot study undertaken on the tropical north west of Venezuela assessed the effect of defoliation interval on herbage quality of maralfalfa grass. The study included three defoliation frequencies (3, 6 and 9 weeks). Treatments were replicated three times in a randomized block design. Measurements included total nitrogen (TN), soluble nitrogen as % of total nitrogen (SN/TN), in Vitro dry matter digestibility (IVDMD), cell wall content (CWC), lignin (L) and total nonstructural carbohydrates (TNC). Data were subjected to analysis of variance, using general linear models procedures of SAS statistical package. Treatments means were contrasted using Tukey test. Nutritive quality of maralfalfa grass declined from three to nine weeks of growth. At each interval TN, CP content declined significantly (P<0.05). NS/NT declined slowly from 3 to 9 weeks, however, in all treatments, over 50% of N was soluble. CWC and L only increased significantly (p<0.05) between six and nine weeks. The highest value of IVDMD (62.45%) was obtained on three weeks of growth and declined on 10.35 digestible units from 3 to 9 weeks. TNC concentrations increased linearly as defoliation interval increased. Values for TNC concentrations ranged from 13.5 to 20.1 % for 3 and 9 weeks, respectively. This study showed that the quality of maralfalfa grass becomes less favorable with advanced maturity, this could be due to increased and accumulation of dead tissue and the lignification of the cell walls. It is suggested that maralfalfa grass be harvested at about sis weeks of growth to optimize nutritive value.